Data center coolant switch

ABSTRACT

A data center cooling system has an indoor portion wherein heat is absorbed from components in the data center, and an outdoor heat exchanger portion wherein outside air is used to cool a first heat transfer fluid (e.g., water) present in at least the outdoor heat exchanger portion of the cooling system during a first mode. When an appropriate time has been reached to switch from the first mode to a second mode, the outdoor heat exchanger portion of the data cooling system is switched to a second heat transfer fluid, which is a relatively low performance heat transfer fluid (compared to the first fluid). It has a second heat transfer fluid freezing point, lower than the first heat transfer fluid freezing point, and sufficiently low to operate without freezing when the outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.:DE-EE0002894 (Department of Energy (DOE). The Government has certainrights in this invention.

FIELD OF THE INVENTION

The present invention relates to the thermodynamic arts, and, moreparticularly, to thermal control of computer equipment and the like.

BACKGROUND OF THE INVENTION

Ambient air cooling (also known as air-side economizers) has beenproposed to reduce data center power consumption. In any locale whereoutdoor ambient temperatures below freezing are anticipated, anantifreeze solution (typically glycol-based) is required within thecoolant loop that is exposed to the ambient environment, so as to avoidfreeze-up if the loop circulation stops for any reason. This antifreezesolution is not as effective in thermal transport as water alone, withthe degree of ineffectiveness varying depending on the exact characterof the devices putting heat into the coolant loop. This lower efficiencycan be significant when attempting to allow for ambient air cooling athigh ambient temperatures, adding cost and complexity to the systemsbeing cooled with the coolant loop.

SUMMARY OF THE INVENTION

Principles of the invention provide techniques for a data center coolantswitch. In one aspect, an exemplary method includes the step ofoperating a data center cooling system in a first mode. The data centercooling system has an indoor portion wherein heat is absorbed fromcomponents in the data center, and the data center cooling system has anoutdoor heat exchanger portion wherein outside air is used to cool afirst heat transfer fluid present in at least the outdoor heat exchangerportion of the cooling system during the first mode. The first heattransfer fluid is a relatively high performance heat transfer fluid, andthe first heat transfer fluid has a first heat transfer fluid freezingpoint. Another step includes determining that an appropriate time hasbeen reached to switch from the first mode to a second mode. A furtherstep includes, responsive to the determining, switching the outdoor heatexchanger portion of the data cooling system to a second heat transferfluid, in preparation for operation in the second mode. The second heattransfer fluid is a relatively low performance heat transfer fluid, andthe second heat transfer fluid has a second heat transfer fluid freezingpoint lower than the first heat transfer fluid freezing point. Thesecond heat transfer fluid freezing point is sufficiently low to operatewithout freezing when the outdoor air temperature drops below a firstpredetermined relationship with the first heat transfer fluid freezingpoint.

In another aspect, a data center cooling system includes an indoorportion wherein heat is absorbed from components in the data center; andan outdoor heat exchanger portion wherein outside air is used to cool afirst heat transfer fluid present in at least the outdoor heat exchangerportion of the cooling system during a first mode of operation. Thefirst heat transfer fluid is a relatively high performance heat transferfluid, and the first heat transfer fluid has a first heat transfer fluidfreezing point. Also included is a coolant switch arrangement configuredto switch the outdoor heat exchanger portion of the data cooling systemto a second heat transfer fluid during a second mode of operation. Thesecond heat transfer fluid is a relatively low performance heat transferfluid, and the second heat transfer fluid has a second heat transferfluid freezing point lower than the first heat transfer fluid freezingpoint. The second heat transfer fluid freezing point is sufficiently lowto operate the outdoor heat exchanger portion of the data center coolingsystem without freezing when the outdoor air temperature drops below afirst predetermined relationship with the first heat transfer fluidfreezing point.

As used herein, “facilitating” an action includes performing the action,making the action easier, helping to carry the action out, or causingthe action to be performed. Thus, by way of example and not limitation,instructions executing on one processor might facilitate an actioncarried out by instructions executing on a remote processor, by sendingappropriate data or commands to cause or aid the action to be performed;or by sending signals to control a valve, fan, or the like, based onsensed temperature, pressure, flow, or the like. For the avoidance ofdoubt, where an actor facilitates an action by other than performing theaction, the action is nevertheless performed by some entity orcombination of entities.

One or more embodiments of the invention or elements thereof (forexample, system control and/or system design) can be implemented in theform of, or otherwise facilitated by, a computer program productincluding a computer readable storage medium with computer usableprogram code for performing the method steps indicated. Furthermore, oneor more embodiments of the invention or elements thereof can beimplemented in the form of a system (or apparatus) including a memory,and at least one processor that is coupled to the memory and operativeto perform exemplary method steps. Yet further, in another aspect, oneor more embodiments of the invention or elements thereof can beimplemented in the form of means for carrying out one or more of themethod steps described herein; the means can include (i) hardwaremodule(s), (ii) software module(s) stored in a computer readable storagemedium (or multiple such media) and implemented on a hardware processor,or (iii) a combination of (i) and (ii); any of (i)-(iii) implement thespecific techniques set forth herein. Examples of use of a computerprogram product or computer-related means include sending signals tocontrol a valve, fan, or the like, based on sensed temperature,pressure, flow, or the like; and/or use of a computer for computer-aidedsystem design.

Techniques of the present invention can provide substantial beneficialtechnical effects. In one or more embodiments, a significant technicalbenefit is the ability to operate both winter and summer with lowercost, higher performance cooling in the summer provided by the watercoolant and freeze resistance in the winter provided by the anti-freezesolution (glycol) utilized when the lower performance of this solutionis not detrimental to system temperature issues.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary data center liquid cooling system, accordingto an aspect of the invention;

FIGS. 2-5 show four stages in operation of the system of FIG. 1;

FIG. 6 shows a flow chart for operation of the system of FIG. 1;

FIG. 7 shows another exemplary data center liquid cooling system,according to an aspect of the invention;

FIG. 8 shows still another exemplary data center liquid cooling system,according to an aspect of the invention;

FIGS. 9-13 show five stages in operation of the system of FIG. 8;

FIG. 14 shows a flow chart for operation of the system of FIG. 8;

FIG. 15 shows a further exemplary data center liquid cooling system,according to an aspect of the invention;

FIGS. 16-20 show five stages in operation of the system of FIG. 15;

FIG. 21 shows a flow chart for operation of the system of FIG. 15; and

FIG. 22 depicts a computer system that may be useful in implementing oneor more aspects and/or elements of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One or more embodiments provide a system that switches between a firstcoolant, such as water, and a second coolant, such as an antifreezesolution, in a coolant loop. In some instances, water is used during thehigh temperature portion of the year and an antifreeze solution is usedduring the low temperature portion of the year. When the temperatureoutside is lower, the lower thermal efficiency of the antifreezesolution can be tolerated. Lower thermal efficiency in this contextmeans a net higher temperature differential between the devices beingcooled and the ambient air temperature and/or a higher power cost tomove and remove the heat from the coolant. In the case of a glycol mix,its higher viscosity requires more power to move the same fluid and itslower ability to conduct and carry heat means a higher temperature drop(higher operating temperature) for the same coolant flow rate.

In one or more instances, the system is implemented by adding a seriesof shut-off valves (which can be computer controlled in some cases) tothe coolant loop, along with a storage tank for the antifreeze solution.The valves can, in at least some instances, be located near the inlet ofthe coolant recirculation pump. When switching from water to antifreeze,the return flow from the system being cooled is directed out of the loopfor appropriate discard or storage using one “shut-off” valve structure.At another downstream location, a similar “shut-off” valve structure isfed with the antifreeze solution. When antifreeze solution begins toappear at the discard/storage outlet, the valves are returned to thenormal circulation position and the swap is complete. The procedure isrepeated, reversing the positions of the water and antifreeze, toreplace the antifreeze with water for higher ambient temperatureenvironments.

Reference will now be made to certain figures to illustrate the workingand implementation of one or more embodiments of a coolant switchingdesign and control technique for same.

FIG. 1 shows an exemplary embodiment in the context of a liquid cooleddata center 100 with an air-side economizer 102, including outside heatexchanger 103 wherein fan 105 blows outside air across the heatexchanger 103 to cool the heat transfer fluid in the cooling loop. Thesystem being cooled includes a liquid cooled rack 104 and a side carsegment 106 (the side car segment is an air-to-liquid heat exchanger,basically a radiator similar to a car's radiator) and is present insidethe data center 100. The storage tanks for the high thermal performancecoolant (such as water) and for the anti-freeze solution (low thermalperformance, for example, Glycol) are also installed inside the datacenter housing and are designated as 108 (high performance) and 110 (lowperformance). The storage tanks are connected to the cooling loop withthe help of a series of shut-off valves 112, 114, 116, 118, 120 that canbe computer controlled. In the case of computer controlled shut-offvalves, the outdoor air temperature (measured at temperature sensor 109)as well as the coolant temperature going to the system (measured attemperature sensor 107) will be used as an input for the shut-off valvecontrol technique. Note the pump 111. The large arrows indicate thedirection of fluid flow. The working of this particular implementationis schematically explained through FIGS. 2-6. In FIGS. 2-5, shaded dotsmean that the valve is closed and a white dot means the valve is open.The dots 9999 in FIGS. 1, 7, 8, and 15 represent pipe connectors and thegap there-between is not intended to suggest a physical gap in thepipes, but rather to delineate that the portion of the given figure thatis on the left of the dots represents an IT rack while the portion ofthe given figure on the right of the dots represent the piping schemefor the coolant switch operation of one or more embodiments.

FIG. 2 represents stage 1 which is normal system operation stage with ahigh thermal performance coolant (such as water) in the cooling loop. Inthis stage, Valve 1, 112, is open and all other valves 114, 116, 118,120 are closed. FIG. 3 represents stage 2 which is the stage ofanti-freeze insertion into the cooling loop. At this stage, Valve 1,112, is closed and Valves 2 and 4 114, 118 are open to allow the highthermal performance coolant (such as water) to drain out to storage tank108 and to allow an anti-freeze solution (such as Glycol) to flow outfrom the storage tank 110 into the cooling loop. The amount ofanti-freeze solution flowing into the system as well as the waterflowing out of the system is monitored using fluid level sensors L1 andL2, 122, 124, respectively. The outputs from these fluid level sensorscan also act as inputs for the control technique to initiate the openingand closing of certain valves. FIG. 4 represents Stage 3 which is thenormal system operation stage with anti-freeze solution in the coolingloop. At this stage, the Valve 1, 112, is open and all other Valves 114,116, 118, 120 are closed. FIG. 5 represents stage 4 which is the switchback to high thermal performance coolant (water insertion) stage. Atthis stage, Valve 1, 112, is closed and Valves 3 and 5, 116, 120respectively, are open to allow the anti-freeze solution (Glycol) todrain out to storage tank 10 and to allow high thermal performancecoolant (water) to flow out from storage tank 108 into the cooling loop.The amount of anti-freeze solution flowing out of the cooling loop aswell as water flowing into the cooling loop system is monitored usingfluid level sensors L1, L2 (122, 124).

FIG. 6 is a flowchart that explains the working of the coolant switchbased on the outdoor air temperature. The cooling system can beinitiated from any stage, however for simplicity; stage 1 (FIG. 2) isrepresented as the initial state of the cooling system, at 602. Theoutdoor air temperature is constantly monitored, as at 604, and based onthis temperature, the exemplary coolant switch process can be activated.In particular, if the outdoor air temperature is greater than thefreezing point T_(FP1) of water or other high performance coolant, plusa suitable safety margin ΔT₁, as per the “Y” branch of block 604,continue with water or other high performance coolant in the loop, as at606, and continue to monitor.

However, when the outdoor air temperature drops below a certaintemperature check point (T_(FP1)+ΔT₁), “N” branch of block 604, theanti-freeze solution (Glycol) insertion stage (FIG. 3) is initiated bythe opening of Valves 2 and 4, 114, 118 and closing of Valve 1, 112, asin step 608. The amount of anti-freeze solution (Glycol) flowing intothe cooling loop and the amount of Water flowing out of the system aremonitored using the fluid level sensors L1 and L2, 112, 124respectively, as in step 610. If insertion is not completed, as per the“N” branch of block 610, keep the valves in the state just described, atstep 612, and continue monitoring. Once the required amount ofanti-freeze is dispersed into the cooling loop (or rather, when theanti-freeze insertion is complete), the next stage (stage 3, FIG. 4) isactivated in step 614, by closing Valves 2 and 4, 114, 118, and byopening Valve 1, 112 simultaneously, as in step 614.

The cooling system operates at this stage, as indicated at 616, untilthe outdoor air temperature goes above a certain temperature check point(freezing point of water or other high performance coolant plus anothersuitable safety margin) (T_(FP1)+ΔT₂). Note the checking in step 618. Ifthe outdoor air has not gone above this temperature, as per the “N”branch of block 618, continue with anti-freeze in the loop. When theoutdoor air temperature goes above this temperature check point(T_(FP1)+ΔT₂), as per the “Y” branch of block 618, the water insertionstage (stage 4, FIG. 5) is activated as per step 620 by the opening ofvalves 3 and 5, 116, 120, and closing of Valve 1, 112. The amount ofwater flowing into the cooling loop and the amount of anti-freezesolution (Glycol) flowing out of the system are monitored using thefluid level sensors L2 and L1, 124, 122 respectively, as at 622. Ifinsertion is not completed, as per the “N” branch of block 622, keep thevalves in the state just described, at step 624, and continuemonitoring. Once the required amount of water is dispersed into thecooling loop (or rather, when the water insertion is complete), as perthe “Y” branch of block 622, the next stage (stage 1, FIG. 2) isactivated, as indicated at 626, by closing Valves 3 and 5 116, 120 andby opening Valve 1, 112, simultaneously.

The cooling system operates at this stage, as indicated by the logicalflow back to step 606, until the outdoor air temperature goes below acertain temperature check point (T_(FP1)+ΔT₁), as described with respectto 604, 606, 608. Once started, the process repeats itself based on theoutdoor air temperature. This coolant switching operation can take placetwo or more times a year depending upon location of the system, weatherconditions of the location and other environmental factors.

FIG. 7 is another possible way of implementing the coolant switchingprocess in a liquid cooled data center 100 with an air-side economizer102. Similar elements in the figures have received the same referencecharacter. The system being cooled includes liquid cooled rack 104 andside car segment 106 and is present inside the data center 100. Theindoor components of this embodiment include liquid-to-liquid heatexchanger 799 in addition to the indoor components depicted in FIG. 1.The presence of the liquid-to-liquid heat exchanger 799 helps de-couplethe cooling loops into an indoor cooling loop 797 and an outdoor coolingloop 795. However, having two cooling loops necessitates the installmentof an additional pump, such that the system includes pump 1, 793, forthe indoor loop and pump 2 791 for the outdoor loop. As depicted in FIG.7, the indoor cooling loop stays completely inside the data centerhousing while the outdoor loop stays partially indoors and partiallyoutdoors.

Thus, the indoor cooling loop 797 can run with the high thermalperformance coolant in the loop under all outside air temperatureconditions. The outdoor loop 795, on the other hand, will requirecoolant switching based on the environmental conditions as well as basedon specific application requirements. The storage tanks for the highthermal performance coolant (such as water) and for the anti-freezesolution (low thermal performance, for example, Glycol) are installed onthe outdoor cooling loop, as shown at 108, 110, respectively, and arealso installed inside the data center housing. The storage tanks areconnected to the cooling loop with the help of a series of shut-offvalves 112, 114, 116, 118, 120 that can be computer controlled. In caseof computer controlled shut-off valves, the outdoor air temperature,measured at 109, as well as the coolant temperature going to the system,measured at 107, will be used as an input for the shut-off valve controltechnique. The working of this particular implementation is similar tothat of the design presented in FIG. 1 and is schematically explainedthrough FIGS. 2-6 described above. It is to be noted here that with thisaspect, there could be slight mixing of the two coolants during theswitching operation.

FIG. 8 schematically represents another method of implementing coolantswitching techniques in a liquid cooled data center 800 with an air-sideeconomizer 802. The configuration of FIG. 8 may appear to be a hybridbetween the configurations shown in FIG. 1 and FIG. 7. However, it usesa different process to switch between the coolants. Moreover, in thisprocess, there is no mixing or other physical interaction between thetwo coolants as the two coolants run inside different cooling loops. Inparticular, this embodiment employs a partial water (high thermalperforming coolant) cooling loop 851 with an outside heat exchanger(outside heat exchanger 2, 855) and two three-way valves 857, 859(arrows indicate flow direction) in addition to the indoor- andoutdoor-cooling loops. The two three-way valves help toggle the flow inthe water loop 851. The system being cooled includes liquid cooled rack104 and side car segment 106 and is present inside the data center 800.In addition, the indoor components of this design includeliquid-to-liquid heat exchanger 899, a water (high thermal performancecoolant) flush tank 861 and the two three-way valves 857, 859. Note alsothe outdoor heat exchanger 856 of the glycol loop.

The presence of liquid-to-liquid heat exchanger 899 helps de-couple thecooling loops into a high thermal performance coolant (water) loop 851and outdoor anti-freeze solution (Glycol) loop 853. However, having twocooling loops necessitates the installment of an additional pump 863 inthe outdoor anti-freeze solution (Glycol) loop; note also pump 865 inthe indoor water loop. As depicted in FIG. 8, the water loop has twoparts; one part 867 that stays completely inside the data center housingand the other part 869 that leads to the outside. Since the loop 869goes to the outside, during cold weather, it is emptied into the flushtank 861 with the help of a gravity assisted drain (not shown to avoidclutter; can be readily implemented by positioning tank 861 at the lowpoint in the loop). The flush tank 861 as well as the pipe loop 869 canhave air release vents 871, 873 to assist gravity drain of water intothe flush tank 861. The outdoor anti-freeze solution loop 853 stayspartially indoors and partially outdoors. For higher temperature ambientenvironments, the loop 869 stays operational and the outdoor anti-freezesolution loop 853 will stay in an OFF state. On the other hand, forlower temperature ambient environments, water flow is directed throughthe liquid-to-liquid heat exchanger 899, the anti-freeze solution loop853 is active, and the air release vents 871, 873 on the loop 869 andflush tank 861 are opened to empty the coolant from the loop 869 intothe flush tank. Fluid temperature sensor 807 represents one or moresensors which measure the coolant temperature of the water in loop 869or glycol or the like in loop 853, as the case may be. The working ofthis particular implementation is schematically explained through FIGS.9-14.

FIG. 9 represents Stage A which is normal system operation stage with ahigh thermal performance coolant (Water) loop operation. In this stage,the 3-Way control valves 857, 859 are oriented in a way so as to directthe water flow through the loop 869. The air release vents 871, 873 areclosed. There is no water flow through the liquid-to-liquid heatexchanger 899. Moreover, the anti-freeze solution loop 853 is notactive, i.e., the outside heat exchanger 856 and the pump 863 are shutOFF. FIGS. 10 through 12 represent the anti-freeze solution (Glycol)loop activation. FIG. 10 represents Stage B1 which is the first step inanti-freeze loop activation. At this stage, the pump 863 and outsideheat exchanger 856 are powered ON to circulate the flow through theanti-freeze loop 853. The loop 869 is still active, the air releasevents 871, 873 are closed, and there is no water flow through theliquid-to-liquid heat exchanger 899.

FIG. 11 represents Stage B2 at which the anti-freeze loop 853 iscompletely active and the three-way valves 857, 859 are turned to directthe water flow through the liquid-to-liquid heat exchanger 899. At thisstage, the outside heat exchanger 855 is still powered ON and the airrelease vents 871, 873 are still closed. FIG. 12 represents stage B3 atwhich the anti-freeze loop 853 is completely active, the three-wayvalves 857, 859 are completely turned to direct the flow through theliquid-to-liquid heat exchanger 899, the outside heat exchanger 855 ispowered OFF and the air release vents 871, 873 are opened to assistgravity drain of water into the flush tank 861. The only flow in theloop 869 is due to water dripping down into the flush tank 861 bygravity. FIG. 13 represents Stage C at which the water through the loop869 is activated. At this stage, all the air release vents 871, 873 areclosed, the outside heat exchanger 855 is powered ON and the three-wayvalves 857, 859 are turned to direct the water flow through the loop869. The Glycol loop 853 is still active with the pump 863 and outsideheat exchanger 856 powered ON. The completely active loop 869 is thesame as stage A (FIG. 9).

FIG. 14 is a flowchart that explains the working of the coolant switchsystem presented in FIG. 8 based on the outdoor air temperature. Thecooling system can be initiated from any stage, however for simplicity;Stage A (FIG. 9) is represented as the initial state of the coolingsystem, as at 1402. The outdoor air temperature is constantly monitoredwith sensor 109, as indicated at 1404, and based on this temperature theexemplary coolant switch process can be activated. In particular, if theoutdoor air temperature is greater than the freezing point T_(FP1) ofwater or other high performance coolant, plus a suitable safety marginΔT₁, as per the “Y” branch of block 1404, continue with water or otherhigh performance coolant in the loop, as at 1406, and continue tomonitor.

When the outdoor air temperature drops below a certain temperature checkpoint (T_(FP1)+ΔT₁), the anti-freeze solution (Glycol) loop activationstage (Stage B1, FIG. 10) is initiated, at 1408, from the “N” branch ofblock 1404, by powering pump 863 and outside heat exchanger 856 ON. Oncethe anti-freeze solution circulation is completely active, the nextstage (stage B2, FIG. 11) is activated by turning the 3-way valves so asto direct the water flow through the liquid/liquid heat exchanger, asalso indicated in step 1408. At this stage, the outside heat exchanger855 is still powered ON and the air release vents 871, 873 are stillclosed. Once the three-way valves are completely turned, the next stage(Stage B3, FIG. 12) is activated as indicated at step 1414 from the “Y”branch of block 1410. Note that if it was determined in step 1410 thatStage B2 was not complete, the turning of the valves would havecontinued in step 1412, “N” branch of block 1410. For the avoidance ofdoubt, note that in step 1410, the position of the 3-way valves isactively monitored. If the desired position of the valves is notachieved, the turning of the valves is continued (step 1412). Once thedesired position of the 3-way valves is achieved, the next stage isactivated

In Stage B3, the anti-freeze loop is completely active, the three-wayvalves 857, 859 are completely turned to direct the flow through theliquid-to-liquid heat exchanger 899, the outside heat exchanger 855 ispowered OFF and the air release vents 871, 873 are opened to assistgravity drain of water into the flush tank 861. The only flow in theloop 869 is due to water dripping down into the flush tank 861 bygravity. As indicated at 1416, the cooling system operates at this stageuntil the outdoor air temperature goes above a certain temperature checkpoint (T_(FP1)+ΔT₂), as determined at 1418 (if not (“N” branch),continue checking; if so (“Y” branch), proceed to 1420). When theoutdoor air temperature goes above this temperature check point(T_(FP1)+ΔT₂), loop 869 activation stage (Stage C, FIG. 13) is started,as at 1420, by closing all the air release vents 871, 873, powering ONthe outside heat exchanger 855 and turning the three-way valves 857, 859to direct the water flow through the loop 869.

At this stage, the Glycol loop 853 is still active with the pump 863 andoutside heat exchanger 856 powered ON. Once the loop 869 is completelyoperational, “Y” branch of block 1422, the glycol loop is turned OFF bypowering the pump 863 and outside heat exchanger 856 OFF. In step 1422,the position of the 3-way valves is actively monitored. If the desiredposition of the valves is not achieved, the turning of the valves iscontinued (step 1424). Once the desired position of the 3-way valves isachieved, the next stage is activated at 1406. For the avoidance ofdoubt, steps 1412 and 1424 indicate that the valves are activelymonitored and controlled.

Moreover, at this next stage, there is no water and glycol flow throughthe liquid-to-liquid heat exchanger 899. The cooling system operates atthis stage, as at 1406, until the outdoor air temperature goes below acertain temperature check point (T_(FP1)+ΔT₁) as explained above withrespect to block 1404. Once started, the process repeats itself based onthe outdoor air temperature. This coolant switching operation can eithertake place for two or more times per year depending upon location of thesystem, weather conditions of the location and other environmentalfactors.

FIG. 15 schematically represents another method of implementing thecoolant switching concept in a liquid cooled data center 1500 with anair-side economizer 1502. This configuration is somewhat similar to theconfiguration shown in FIG. 8 and uses a similar process to switchbetween the coolants. However, this configuration uses only one outsideheat exchanger unit 1555 with two liquid side coils. One liquid coil1557 is for the water loop and the other liquid coil 1559 is for theanti-freeze solution. Moreover, in this process, there is no possiblemixing and/or physical interaction between the two coolants as the twocoolants run inside different cooling loops. This scheme requires apartial water (high thermal performing coolant) cooling loop 1569 withan additional coil in the outside heat exchanger (water coil 1557) andtwo 3-Way valves 1503, 1505 in addition to the indoor- andoutdoor-cooling loops. The two 3-Way valves help toggle the flow in theloop 1569. The system being cooled includes a liquid cooled rack 104 anda side car segment 106 and is present inside the data center 1500. Inaddition, the indoor components of this design include a liquid/liquidheat exchanger 1599, a water (high thermal performance coolant) flushtank 1561 and two 3-way valves 1503, 1505. The presence of aliquid/liquid heat exchanger helps de-couple the cooling loops into ahigh thermal performance coolant (water) loop 1567, 1569 and outdooranti-freeze solution (Glycol) loop 1553. However, having two coolingloops necessitates the installment of an additional pump 1563 in theoutdoor anti-freeze solution (Glycol) loop 1553.

As depicted in FIG. 15, the water loop has two parts—one 1567 that stayscompletely inside the data center housing and the other 1569 that goesto the outside. Since the loop 1569 goes to the outside, during coldweather, it is emptied into the flush tank 1561 with the help of agravity assisted drain (not explicitly shown; can be achieved bylocating tank 1561 at the low point of the water loop). The flush tank1561 and the loop 1569 have air release vents 1571, 1573 to assistgravity drain of water into the flush tank. The outdoor anti-freezesolution loop 1553 stays partially indoor and partially outdoor. Forhigher temperature ambient environments, the loop 1569 will stayoperational and the outdoor anti-freeze solution loop 1553 will stay inan OFF state. On the other hand, for lower temperature ambientenvironments, water flow will be directed through the liquid-to-liquidheat exchanger 1599, the anti-freeze solution loop 1553 will be activeand the air release vents 1571, 1573 on the loop 1569 and flush tank1561 will be opened to empty the coolant from the loop 1569 into theflush tank 1561. Fluid temperature sensor 1507 represents one or moresensors which measure the coolant temperature of the water in loop 1569or glycol or the like in loop 1553, as the case may be. The working ofthis particular implementation is schematically explained throughfigures FIG. 16-FIG. 21. In FIG. 15, note also the pump 1565 for thewater loop 1567, 1569.

FIG. 16 represents Stage (i) which is a normal system operation stagewith high thermal performance coolant (Water) loop operation; i.e., loop1569 operates. In this stage, the 3-way control valves 1503, 1505, areoriented in a way so as to direct the water flow through the loop 1569.The air release vents 1571, 1573 on the loop 1569 and on the flush tank1561 are closed. There is no water flow through the liquid-to-liquidheat exchanger 1599. Moreover, the anti-freeze solution loop 1553 is notactive, i.e., the pump 1563 is shut OFF. FIGS. 17-19 represent theanti-freeze solution (Glycol) loop 1553 activation. FIG. 17 representsStage (iiA) which is the first step in anti-freeze loop activation. Atthis stage, the pump 1563 is powered ON to circulate the flow throughthe anti-freeze loop 1553. The loop 1569 is still active, the airrelease vents 1571, 1573 are closed and there is no water flow throughthe liquid-to-liquid heat exchanger 1599. FIG. 18 represents Stage (iiB)at which the anti-freeze loop 1553 is completely active and thethree-way valves 1503, 1505 are turned to direct the water flow throughthe liquid-to-liquid heat exchanger 1599. At this stage, the air releasevents 1571, 1573 are still closed. FIG. 19 represents stage (iiC) atwhich the anti-freeze loop 1553 is completely active, the three-wayvalves 1503, 1505 are completely turned to direct the flow through theliquid-to-liquid heat exchanger 1599 and the air release vents 1571,1573 are opened to assist gravity drain of water into the flush tank1561. The only flow in the loop 1569 is due to water dripping down intothe flush tank 1561 due to gravity. FIG. 20 represents Stage (iii) atwhich the water through the loop 1569 is activated. At this stage, allthe air release vents 1571, 1573 are closed and the three-way valves1503, 1505 are turned to direct the water flow through the loop 1569.The Glycol loop 1553 is still active with the pump 1563 and outside heatexchanger 1559 with fan 105 powered ON. The completely active loop 1569is the same as stage (i) in FIG. 16.

FIG. 21 is a flowchart that explains the working of the coolant switchsystem presented in FIG. 15 based on the outdoor air temperature. Thecooling system can be initiated from any stage, however for simplicity;Stage (i), FIG. 16, is represented as the initial state of the coolingsystem, as at 2102. The outdoor air temperature is constantly monitoredwith sensor 109; based on this temperature the coolant switch processcan be activated. As shown at 2104, when the outdoor air temperaturedrops below a certain temperature check point (T_(FP1)+ΔT₁), theanti-freeze solution (Glycol) loop activation stage (Stage iiA, FIG. 17)is initiated by powering pump 1563 ON, as at 2106 (“N” branch ofdecision block 2104). If decision block 2104 yields a “Y,” simplycontinue with the water loop ON as per 2108.

Once the anti-freeze solution circulation is completely active (“Y”branch of decision block 2110; if block 2110 yields an “N,” then turnthe valves at 2112), the next stage (stage (iiB), FIG. 18) is activatedby turning the three-way valves 1503, 1505 so as to direct the waterflow through the liquid-to-liquid heat exchanger 1599. At this stage,the air release vents 1571, 1573 are still closed. Once the three-wayvalves 1503, 1505 are completely turned, the next stage (Stage (iiC),FIG. 19) is activated, at step 2114. At this stage, the anti-freeze loop1553 is completely active, the three-way valves 1503, 1505 arecompletely turned to direct the flow through the liquid-to-liquid heatexchanger 1599, and the air release vents 1571, 1573 are opened toassist gravity drain of water into the flush tank 1561. The only flow inthe loop 1569 is due to water dripping down into the flush tank 1561 dueto gravity.

As shown at 2116, the cooling system operates at this stage until theoutdoor air temperature goes above a certain temperature check point(T_(FP1)+ΔT₂), as determined in step 2118. When the outdoor airtemperature goes above this temperature check point (T_(FP1)+ΔT₂), asper the “Y” branch of decision block 2118, activation of loop 1569(Stage (iii), FIG. 20) is started, as at 2120, by closing all the airrelease vents 1571, 1573 and turning the three-way valves 1503, 1505 todirect the water flow through the loop 1569. (If block 2118 yields an“N” then control passes back to step 2116.) At this stage, the Glycolloop 1553 is still active with the pump 1563. Once the loop 1569 iscompletely operational, as monitored at steps 2122 and 2124, the glycolloop 1553 is turned OFF by powering pump 1563 OFF. Moreover, at thisstage, there is no water and glycol flow through the liquid-to-liquidheat exchanger 1599. The cooling system operates at this stage, as per2108, until the outdoor air temperature goes below a certain temperaturecheck point (T_(FP1)+ΔT₁). Once started, the process repeats itselfbased on the outdoor air temperature. This coolant switching operationcan either take two or more times a year depending upon location of thesystem, weather conditions of the location and other environmentalfactors. Steps 2110, 2112 and 2122, 2124 represent an active monitoringof the valves, similar to steps 1410, 1412 and 1422, 1424 as discussedabove. It should be noted that other embodiments could possibly use adifferent approach wherein valve actuation was treated in a binaryon-off fashion.

One or more embodiments advantageously provide a method of swappingcoolants in a given coolant loop using shut-off valves and/or three-wayvalves. One or more instances provide the ability to use different(possibly miscible) coolants in the same cooling loop. Four non-limitingexemplary illustrative embodiments for liquid cooling one or more datacenter racks have been disclosed, as has a control algorithm for thecoolant swapping process based on the ambient temperature. High thermalperformance coolant (e.g., water) will be used during the hightemperature portion of the year while relatively low thermal performancecoolant (e.g., glycol or other antifreeze-based solution) will be usedduring the low temperature portion of the year.

For the avoidance of doubt, one or more embodiments swap between twoseparate coolants and do not merely employ two phases (such as liquidand vapor) of the same coolant in the same loop. Furthermore, at leastsome embodiments employ single-phase (liquid) cooling only.

Given the discussion thus far, it will be appreciated that, in generalterms, an exemplary method (e.g., FIGS. 6, 14, 21), according to anaspect of the invention, includes the step of operating a data centercooling system 100, 800, 1500 in a first mode, as at 602, 1402, 2102.The data center cooling system has an indoor portion wherein heat isabsorbed from components (e.g., 104, 106) in the data center. The datacenter cooling system has an outdoor heat exchanger portion 102, 802,1502) wherein outside air is used to cool a first heat transfer fluid(e.g., water) present in at least the outdoor heat exchanger portion ofthe cooling system during the first mode. The first heat transfer fluidis a relatively high performance heat transfer fluid (as compared to thesecond fluid). The first heat transfer fluid has a first heat transferfluid freezing point (32 F or 0 C in the case of water).

For the avoidance of doubt, the outdoor economizer portions depicted inthe figures include a heat exchanger and a fan. However, someembodiments could employ outdoor heat exchanger portions without fans.As used in the claims, an “outdoor heat exchanger portion” is intendedto encompass both an outdoor heat exchanger with a fan (economizer) andan outdoor heat exchanger without a fan.

Another step, e.g., 604, 1404, 2104, includes determining that anappropriate time has been reached to switch from the first mode to asecond mode. In a non-limiting example, this determination could includemonitoring an outdoor air temperature 109 adjacent the outdoor heatexchanger portion of the data center cooling system to determine whetherthe outdoor air temperature has reached a first predeterminedrelationship with the first heat transfer fluid freezing point.

A further step, as at 608, 1408, 2106 includes, responsive to thedetermining step (again, purely by way of example and not limitation,outdoor air temperature reaching the first predetermined relationshipwith the first heat transfer fluid freezing point), switching theoutdoor heat exchanger portion of the data cooling system to a secondheat transfer fluid (e.g., an antifreeze such as ethylene glycol or anantifreeze-water mixture, such as an ethylene glycol-water mixture), inpreparation for operation in the second mode. The second heat transferfluid is a relatively low performance heat transfer fluid, as comparedto the first heat transfer fluid. The second heat transfer fluid has asecond heat transfer fluid freezing point lower than the first heattransfer fluid freezing point, and the second heat transfer fluidfreezing point is sufficiently low to operate without freezing when theoutdoor air temperature drops below a first predetermined relationshipwith the first heat transfer fluid freezing point.

Further optional steps include, as at 616, 1416, 2116, operating thedata center cooling system in the second mode, wherein the outside airis used to cool the second heat transfer fluid present in at least theoutdoor heat exchanger portion of the cooling system during the secondmode; and, as at 618, 1418, 2118, determining that an appropriate timehas been reached to switch from the second mode back to the first mode(purely by way of example and not limitation, monitoring the outdoor airtemperature (the use of a definitive article before “outdoor airtemperature” means the air temperature in the same region; of course itwill not necessarily have the same value) adjacent the outdoor heatexchanger portion of the data center cooling system to determine whetherthe outdoor air temperature has reached a second predeterminedrelationship with the first heat transfer fluid freezing point). A stillfurther optional step 620, 1420, 2120 includes, responsive to thedetermining that the appropriate time has been reached to switch fromthe second mode back to the first mode, switching the outdoor heatexchanger portion of the data cooling system back to the first heattransfer fluid.

In some instances, such as shown in FIG. 1, the data center coolingsystem includes a single loop passing through the data center to theoutdoor heat exchanger portion 102, a first tank 108 to store the firstheat transfer fluid, a second tank 110 to store the second heat transferfluid, and a valve arrangement 112, 114, 116, 118, 120; as describedabove, the valve arrangement is configured to isolate the first andsecond tanks during steady-state operation, allow the first heattransfer fluid to flow from the single loop into the first tank and thesecond heat transfer fluid to flow from the second tank into the singleloop when transitioning from the first mode to the second mode, andallow the second heat transfer fluid to flow from the single loop intothe second tank and the first heat transfer fluid to flow from the firsttank back into the single loop when transitioning from the second modeto the first mode. In such cases, the step of switching the outdoor heatexchanger portion of the data cooling system to the second heat transferfluid includes actuating the valve arrangement to allow the first heattransfer fluid to flow from the single loop into the first tank and thesecond heat transfer fluid to flow from the second tank into the singleloop when transitioning from the first mode to the second mode, and thestep of switching the outdoor heat exchanger portion of the data coolingsystem back to the first heat transfer fluid includes actuating thevalve arrangement to allow the second heat transfer fluid to flow fromthe single loop into the second tank and the first heat transfer fluidto flow from the first tank back into the single loop when transitioningfrom the second mode to the first mode.

In some cases, such as shown in FIG. 7, the data center cooling systemincludes an indoor loop 797 passing through the data center to aliquid-to-liquid heat exchanger 799, an indoor-outdoor loop 795 passingfrom the liquid-to-liquid heat exchanger to the outdoor heat exchangerportion 102, a first tank 108 to store the first heat transfer fluid, asecond tank 110 to store the second heat transfer fluid, and a valvearrangement 112, 114, 116, 118, 120. As described above, the valvearrangement is configured to isolate the first and second tanks duringsteady-state operation, allow the first heat transfer fluid to flow fromthe indoor-outdoor loop into the first tank and the second heat transferfluid to flow from the second tank into the indoor-outdoor loop whentransitioning from the first mode to the second mode, and allow thesecond heat transfer fluid to flow from the indoor-outdoor loop into thesecond tank and the first heat transfer fluid to flow from the firsttank back into the indoor-outdoor loop when transitioning from thesecond mode to the first mode. In such cases, the step of switching theoutdoor heat exchanger portion of the data cooling system to the secondheat transfer fluid includes actuating the valve arrangement to allowthe first heat transfer fluid to flow from the indoor-outdoor loop intothe first tank and the second heat transfer fluid to flow from thesecond tank into the indoor-outdoor loop when transitioning from thefirst mode to the second mode, and the step of switching the outdoorheat exchanger portion of the data cooling system back to the first heattransfer fluid includes actuating the valve arrangement to allow thesecond heat transfer fluid to flow from the indoor-outdoor loop into thesecond tank and the first heat transfer fluid to flow from the firsttank back into the indoor-outdoor loop when transitioning from thesecond mode to the first mode.

In some embodiments, such as FIG. 8 or 15, the data center coolingsystem includes a first heat transfer fluid indoor loop 867, 1567passing through the data center; a liquid-to-liquid heat exchanger 899,1599 selectively coupled to the first heat transfer fluid indoor loop; afirst heat transfer fluid indoor-outdoor loop 869, 1569 selectivelyconnectable to the first heat transfer fluid indoor loop and coupled tothe outdoor heat exchanger portion; and a second heat transfer fluidloop 853, 1553 passing from the liquid-to-liquid heat exchanger to theoutdoor heat exchanger portion. Also included is a valve arrangement857, 859, 1505, 1503 configured to couple the first heat transfer fluidindoor loop to the first heat transfer fluid indoor-outdoor loop duringsteady-state operation in the first mode; and couple the first heattransfer fluid indoor loop to the liquid-to-liquid heat exchanger duringsteady-state operation in the second mode. The step of switching theoutdoor heat exchanger portion of the data cooling system to the secondheat transfer fluid includes actuating the valve arrangement to couplethe first heat transfer fluid indoor loop to the liquid-to-liquid heatexchanger; and the step of switching the outdoor heat exchanger portionof the data cooling system back to the first heat transfer fluidincludes actuating the valve arrangement to couple the first heattransfer fluid indoor loop to the first heat transfer fluidindoor-outdoor loop.

As noted, the determining steps can include monitoring an outdoor airtemperature adjacent the outdoor heat exchanger portion of the datacenter cooling system to determine whether the outdoor air temperaturehas reached the first predetermined relationship with the first heattransfer fluid freezing point; however, many other approaches arepossible, such as determining that a particular calendar day has beenreached, making a determination based on local meteorological data, andthe like. Similar considerations apply to the decision to switch back.Indeed, in general, how the choice is made with regard to switching fromone coolant to another and then switching back can be carried out inmany different ways, such as by calendar, peak or average dailytemperature, or any other suitable method. Furthermore, thepredetermined relationships (ΔT_(FP1) and ΔT_(FP2)) can be chosen, forexample, to intend to limit the number of coolant switch cycles to oneper year. An example might be the low performance coolant would beswitched in when the temperature came within about 10 degrees F. (about5.6 degrees C.) of the freezing point. It might then be switched outwhen the daily low temperature exceeded about 20 degrees F. (about 11degrees C.) over freezing. These are just exemplary numbers which shouldbe chosen utilizing local temperature variations. Alternatively, the lowperformance coolant could be switched out on one date (say May 15th) andin on another (say October 1st). These could be reversed in the SouthernHemisphere, for example.

Thus, as alluded to, the first determining step can, in some instances,include monitoring an outdoor air temperature adjacent the outdoor heatexchanger portion of the data center cooling system to determine whetherthe outdoor air temperature has reached a first predeterminedrelationship with the first heat transfer fluid freezing point, and thesecond determining step can, in some instances, include monitoring theoutdoor air temperature adjacent the outdoor heat exchanger portion ofthe data center cooling system to determine whether the outdoor airtemperature has reached a second predetermined relationship with thefirst heat transfer fluid freezing point. Again, these are non-limitingexamples.

In another aspect, a data center cooling system (FIG. 1, 7, 8, or 15)includes an indoor portion wherein heat is absorbed from components 104,106 in the data center; and an outdoor heat exchanger portion 102, 802,1502 wherein outside air is used to cool a first heat transfer fluidpresent in at least the outdoor heat exchanger portion of the coolingsystem during a first mode of operation. The first heat transfer fluidis a relatively high performance heat transfer fluid, and the first heattransfer fluid has a first heat transfer fluid freezing point.

A further element is a coolant switch arrangement configured to switchthe outdoor heat exchanger portion of the data cooling system to asecond heat transfer fluid during a second mode of operation. The secondheat transfer fluid is a relatively low performance heat transfer fluid,and the second heat transfer fluid has a second heat transfer fluidfreezing point lower than the first heat transfer fluid freezing point.The second heat transfer fluid freezing point is sufficiently low tooperate the outdoor heat exchanger portion of the data center coolingsystem without freezing when the outdoor air temperature drops below afirst predetermined relationship with the first heat transfer fluidfreezing point.

Some instances also include a control unit coupled to the coolant switcharrangement and configured to determine that an appropriate time hasbeen reached to switch from the first mode to the second mode; in suchinstances, the coolant switch arrangement switches the outdoor heatexchanger portion of the data cooling system to the second heat transferfluid responsive to the determination by the control unit. In anon-limiting example, the control unit includes an outdoor airtemperature sensor 109 positioned adjacent the outdoor heat exchangerportion of the data center cooling system to determine whether theoutdoor air temperature has reached the first predetermined relationshipwith the first heat transfer fluid freezing point. The sensor could be,for example, a thermocouple or the like coupled to logic in a processoras described below with regard to FIG. 22. Mechanical orelectromechanical techniques, such as a bimetallic strip with contacts,could also be used. Appropriate logic, such as described with regard toFIG. 22, could also be used to implement any of the other approaches,such as determining that a particular calendar day has been reached(calendar or clock logic in machine 2212), making a determination basedon local meteorological data (e.g., interface to a weather web site orprogramming based on historical data), and the like.

In one or more embodiments, the coolant switch arrangement is furtherconfigured to operate the data center cooling system in the second mode,wherein the outside air is used to cool the second heat transfer fluidpresent in at least the outdoor heat exchanger portion of the coolingsystem during the second mode; the control unit is configured todetermine that an appropriate time has been reached to switch from thesecond mode back to the first mode (e.g., outdoor air temperature sensormonitors the outdoor air temperature adjacent the outdoor heat exchangerportion of the data center cooling system to determine whether theoutdoor air temperature has reached a second predetermined relationshipwith the first heat transfer fluid freezing point); and, responsive tothe control unit determining that the appropriate time has been reachedto switch from the second mode back to the first mode (e.g., outdoor airtemperature reaching the second predetermined relationship with thefirst heat transfer fluid freezing point), the coolant switcharrangement switches the outdoor heat exchanger portion of the datacooling system back to the first heat transfer fluid.

Exemplary first and second heat transfer fluids have been discussedelsewhere.

As seen in FIG. 1, in some cases, the system includes a single looppassing through the data center to the outdoor heat exchanger portion102; a first tank 108 to store the first heat transfer fluid; and asecond tank 110 to store the second heat transfer fluid. In FIG. 1, thecoolant switch arrangement includes a valve arrangement 112, 114, 116,118, 120 configured to isolate the first and second tanks duringsteady-state operation; allow the first heat transfer fluid to flow fromthe single loop into the first tank and the second heat transfer fluidto flow from the second tank into the single loop when transitioningfrom the first mode to the second mode; and allow the second heattransfer fluid to flow from the single loop into the second tank and thefirst heat transfer fluid to flow from the first tank back into thesingle loop when transitioning from the second mode to the first mode.This operation is described above.

As seen in FIG. 7, in some cases, the system includes an indoor loop 797passing through the data center to a liquid-to-liquid heat exchanger799; an indoor-outdoor loop 795 passing from the liquid-to-liquid heatexchanger to the outdoor heat exchanger portion 102; a first tank 108 tostore the first heat transfer fluid; and a second tank 110 to store thesecond heat transfer fluid. Here, the coolant switch arrangementincludes a valve arrangement 112, 114, 116, 118, 120 configured to:isolate the first and second tanks during steady-state operation; allowthe first heat transfer fluid to flow from the indoor-outdoor loop intothe first tank and the second heat transfer fluid to flow from thesecond tank into the indoor-outdoor loop when transitioning from thefirst mode to the second mode; and allow the second heat transfer fluidto flow from the indoor-outdoor loop into the second tank and the firstheat transfer fluid to flow from the first tank back into theindoor-outdoor loop when transitioning from the second mode to the firstmode.

As seen in FIGS. 8 and 15, in some cases, the system includes a firstheat transfer fluid indoor loop 867, 1567 passing through the datacenter; a liquid-to-liquid heat exchanger 899, 1599 selectively coupledto the first heat transfer fluid indoor loop; a first heat transferfluid indoor-outdoor loop 869, 1569 selectively connectable to the firstheat transfer fluid indoor loop and coupled to the outdoor heatexchanger portion; and a second heat transfer fluid loop 853, 1553passing from the liquid-to-liquid heat exchanger to the outdoor heatexchanger portion. The coolant switch arrangement includes a valvearrangement 857, 859 configured to couple the first heat transfer fluidindoor loop to the first heat transfer fluid indoor-outdoor loop duringsteady-state operation in the first mode; and couple the first heattransfer fluid indoor loop to the liquid-to-liquid heat exchanger duringsteady-state operation in the second mode.

In some cases, such as FIG. 8, the outdoor heat exchanger portionincludes a first outside heat exchanger 856 coupled to the second heattransfer fluid loop and a second outside heat exchanger 855 coupled tothe first heat transfer fluid indoor-outdoor loop.

In other cases, such as FIG. 15, the outdoor heat exchanger portioncomprises a single outside heat exchanger having a first coil 1559coupled to the second heat transfer fluid loop and a second coil 1557coupled to the first heat transfer fluid indoor-outdoor loop.

Exemplary System and Article of Manufacture Details

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon. Forthe avoidance of doubt, most embodiments include physical heat transferand fluid flow hardware which may be computer controlled, controlled byhumans, controlled by electromechanical and/or bimetallic controllers,and the like; a software embodiment could include, for example, acomputer readable storage medium with instructions for system controland/or design functionality.

One or more embodiments of the invention, or elements thereof, can beimplemented in the form of an apparatus including a memory and at leastone processor that is coupled to the memory and operative to performexemplary method steps.

One or more embodiments can make use of software running on a generalpurpose computer or workstation. With reference to FIG. 22, such animplementation might employ, for example, a processor 2202, a memory2204, and an input/output interface formed, for example, by a display2206 and a keyboard 2208. The term “processor” as used herein isintended to include any processing device, such as, for example, onethat includes a CPU (central processing unit) and/or other forms ofprocessing circuitry. Further, the term “processor” may refer to morethan one individual processor. The term “memory” is intended to includememory associated with a processor or CPU, such as, for example, RAM(random access memory), ROM (read only memory), a fixed memory device(for example, hard drive), a removable memory device (for example,diskette), a flash memory and the like. In addition, the phrase“input/output interface” as used herein, is intended to include, forexample, one or more mechanisms for inputting data to the processingunit (for example, mouse), and one or more mechanisms for providingresults associated with the processing unit (for example, printer). Theprocessor 2202, memory 2204, and input/output interface such as display2206 and keyboard 2208 can be interconnected, for example, via bus 2210as part of a data processing unit 2212. Suitable interconnections, forexample via bus 2210, can also be provided to a network interface 2214,such as a network card, which can be provided to interface with acomputer network, and to a media interface 2216, such as a diskette orCD-ROM drive, which can be provided to interface with media 2218.

Suitable interfaces can be provided to receive signals from sensors(e.g., temperature, pressure, flow rate, and/or valve position sensors)and/or to send signals to actuators for valves, vents, fans, and thelike. These could be provided over network interface 2214 and/or viaseparate sensor interface 2297 and/or separate actuator interface 2299,including, for example, suitable digital-to-analog and/oranalog-to-digital converters.

Accordingly, computer software including instructions or code forperforming the methodologies of the invention, as described herein, maybe stored in one or more of the associated memory devices (for example,ROM, fixed or removable memory) and, when ready to be utilized, loadedin part or in whole (for example, into RAM) and implemented by a CPU.Such software could include, but is not limited to, firmware, residentsoftware, microcode, and the like.

A data processing system suitable for storing and/or executing programcode will include at least one processor 2202 coupled directly orindirectly to memory elements 2204 through a system bus 2210. The memoryelements can include local memory employed during actual implementationof the program code, bulk storage, and cache memories which providetemporary storage of at least some program code in order to reduce thenumber of times code must be retrieved from bulk storage duringimplementation.

Input/output or I/O devices (including but not limited to keyboards2208, displays 2206, pointing devices, and the like) can be coupled tothe system either directly (such as via bus 2210) or through interveningI/O controllers (omitted for clarity).

Network adapters such as network interface 2214 may also be coupled tothe system to enable the data processing system to become coupled toother data processing systems or remote printers or storage devicesthrough intervening private or public networks. Modems, cable modem andEthernet cards are just a few of the currently available types ofnetwork adapters.

As used herein, including the claims, a “server” includes a physicaldata processing system (for example, system 2212 as shown in FIG. 22)running a server program. It will be understood that such a physicalserver may or may not include a display and keyboard.

As noted, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon. Anycombination of one or more computer readable medium(s) may be utilized.The computer readable medium may be a computer readable signal medium ora computer readable storage medium. A computer readable storage mediummay be, for example, but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,or device, or any suitable combination of the foregoing. Media block2218 is a non-limiting example. More specific examples (a non-exhaustivelist) of the computer readable storage medium would include thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), an optical fiber, a portable compact disc read-onlymemory (CD-ROM), an optical storage device, a magnetic storage device,or any suitable combination of the foregoing. In the context of thisdocument, a computer readable storage medium may be any tangible mediumthat can contain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

It should be noted that any of the methods described herein can includean additional step of providing a system comprising distinct softwaremodules embodied on a computer readable storage medium; the modules caninclude, for example, one or more distinct software modules for control(e.g., to control the cooling systems using the logic in the flowcharts) and/or system design. The method steps can then be carried out,or at least facilitated by, using the distinct software modules and/orsub-modules of the system, as described above, executing on one or morehardware processors 2202. Further, a computer program product caninclude a computer-readable storage medium with code adapted to beimplemented to carry out one or more method steps described herein,including the provision of the system with the distinct softwaremodules.

In any case, it should be understood that the components illustratedherein may be implemented in various forms of hardware, software, orcombinations thereof for example, application specific integratedcircuit(s) (ASICS), functional circuitry, one or more appropriatelyprogrammed general purpose digital computers with associated memory, andthe like. Given the teachings of the invention provided herein, one ofordinary skill in the related art will be able to contemplate otherimplementations of the components of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A system comprising: an indoor portion whereinheat is absorbed from components in a data center during a first mode;an outdoor heat exchanger portion wherein outside air is used to cool afirst heat transfer fluid present in at least the outdoor heat exchangerportion during the first mode, the first heat transfer fluid having afirst freezing point; a control unit configured to determine that anappropriate condition is met to switch from the first mode to a secondmode, wherein the appropriate condition is a threshold condition; aswitch configured to switch from the first mode to the second mode, theswitch switching the outdoor heat exchanger portion to a second heattransfer fluid, in preparation for operation in the second mode; andwherein the second heat transfer fluid has a second freezing point lowerthan the first freezing point, wherein the second freezing point islower than a lowest expected outdoor operating air temperature.
 2. Thesystem of claim 1, wherein the outside air is used to cool the secondheat transfer fluid present in at least the outdoor heat exchangerportion during the second mode, wherein the control unit is configuredto determine that a second appropriate condition has been met to switchfrom the second mode back to the first mode, and wherein the switchresponsive to the control unit determining that the second appropriatecondition is met to switch from the second mode back to the first mode,is configured to switch the outdoor heat exchanger portion back to thefirst heat transfer fluid.
 3. The system of claim 1 wherein: the firstheat transfer fluid comprises water; and the second heat transfer fluidcomprises one of antifreeze and an antifreeze-water mixture.
 4. Thesystem of claim 3, wherein the antifreeze comprises ethylene glycol andthe antifreeze-water mixture comprises an ethylene glycol-water mixture.5. The system of claim 1, further comprising: a single loop passingthrough the data center to the outdoor heat exchanger portion; a firsttank to store the first heat transfer fluid; and a second tank to storethe second heat transfer fluid; wherein the switch comprises a valvearrangement configured to: isolate the first and second tanks duringsteady-state operation; allow the first heat transfer fluid to flow fromthe single loop into the first tank and the second heat transfer fluidto flow from the second tank into the single loop when transitioningfrom the first mode to the second mode; and allow the second heattransfer fluid to flow from the single loop into the second tank and thefirst heat transfer fluid to flow from the first tank back into thesingle loop when transitioning from the second mode to the first mode.6. The system of claim 1, further comprising: an indoor loop passingthrough the data center to a liquid-to-liquid heat exchanger; anindoor-outdoor loop passing from the liquid-to-liquid heat exchanger tothe outdoor heat exchanger portion; a first tank to store the first heattransfer fluid; and a second tank to store the second heat transferfluid; and wherein the switch comprises a valve arrangement configuredto: isolate the first and second tanks during steady-state operation;allow the first heat transfer fluid to flow from the indoor-outdoor loopinto the first tank and the second heat transfer fluid to flow from thesecond tank into the indoor-outdoor loop when transitioning from thefirst mode to the second mode; and allow the second heat transfer fluidto flow from the indoor-outdoor loop into the second tank and the firstheat transfer fluid to flow from the first tank back into theindoor-outdoor loop when transitioning from the second mode to the firstmode.
 7. The system of claim 1 further comprising: a first heat transferfluid indoor loop passing through the data center; a liquid-to-liquidheat exchanger selectively coupled to the first heat transfer fluidindoor loop; a first heat transfer fluid indoor-outdoor loop selectivelyconnectable to the first heat transfer fluid indoor loop and coupled tothe outdoor heat exchanger portion; and a second heat transfer fluidloop passing from the liquid-to-liquid heat exchanger to the outdoorheat exchanger portion; wherein the switch comprises a valve arrangementconfigured to: couple the first heat transfer fluid indoor loop to thefirst heat transfer fluid indoor-outdoor loop during steady-stateoperation in the first mode; and couple the first heat transfer fluidindoor loop to the liquid-to-liquid heat exchanger during steady-stateoperation in the second mode.
 8. The system of claim 7, wherein theoutdoor heat exchanger portion comprises a first outside heat exchangercoupled to the second heat transfer fluid loop and a second outside heatexchanger coupled to the first heat transfer fluid indoor-outdoor loop.9. The system of claim 7, wherein the outdoor heat exchanger portioncomprises a single outside heat exchanger having a first coil coupled tothe second heat transfer fluid loop and a second coil coupled to thefirst heat transfer fluid indoor-outdoor loop.
 10. The system of claim1, wherein the control unit comprises an outdoor air temperature sensorpositioned adjacent the outdoor heat exchanger portion of the datacenter cooling system to determine whether the outdoor air temperaturehas reached the first predetermined relationship with the first heattransfer fluid freezing point.
 11. A method comprising: operating a datacenter cooling system in a first mode, wherein the data center coolingsystem has an indoor portion wherein heat is absorbed from components inthe data center, and wherein the data center cooling system has anoutdoor heat exchanger portion, wherein outside air is used to cool afirst heat transfer fluid present in at least the outdoor heat exchangerportion during the first mode, wherein the first heat transfer fluid hasa first freezing point; determining that an appropriate condition is metto switch from the first mode to a second mode wherein the appropriatecondition is a threshold condition; and switching, responsive to thedetermining, the outdoor heat exchanger portion to a second heattransfer fluid, in preparation for operation in the second mode, thesecond heat transfer fluid having a second freezing point lower than thefirst freezing point, wherein the second freezing point is lower than alowest expected outdoor operating air temperature.
 12. The method ofclaim 11, further comprising: operating the data center cooling systemin the second mode, wherein the outside air is used to cool the secondheat transfer fluid present in at least the outdoor heat exchangerportion during the second mode; determining that a second appropriatecondition is met to switch from the second mode back to the first mode;and switching, responsive to the determining that the second appropriatecondition is met to switch from the second mode back to the first mode,the outdoor heat exchanger portion back to the first heat transferfluid.
 13. A data center cooling system comprising: an indoor portionwherein heat is absorbed from components in the data center; an outdoorheat exchanger portion wherein outside air is used to cool a first heattransfer fluid present in at least the outdoor heat exchanger portion ofthe cooling system during a first mode of operation, the first heattransfer fluid is a relatively high performance heat transfer fluid, thefirst heat transfer fluid having a first freezing point; and a coolantswitch arrangement configured to switch the outdoor heat exchangerportion of the data cooling system to a second heat transfer fluidduring a second mode of operation, the second heat transfer fluid beinga relatively low performance heat transfer fluid, the second heattransfer fluid having a second freezing point lower than the first heattransfer fluid freezing point, and wherein the second freezing point islower than a lowest expected outdoor operating air temperature; andwherein the relatively high performance heat transfer fluid has agreater efficiency in transferring heat than the relatively lowperformance heat transfer fluid.
 14. The system of claim 1, furthercomprising a control unit coupled to the coolant switch arrangement andconfigured to determine that an appropriate time has been reached toswitch from the first mode to the second mode, wherein the coolantswitch arrangement switches the outdoor heat exchanger portion of thedata cooling system to the second heat transfer fluid responsive to thedetermination by the control unit.
 15. The system of claim 14, wherein:the coolant switch arrangement is further configured to operate the datacenter cooling system in the second mode, wherein the outside air isused to cool the second heat transfer fluid present in at least theoutdoor heat exchanger portion of the cooling system during the secondmode; the control unit is configured to determine that a secondappropriate time has been reached to switch from the second mode back tothe first mode; and responsive to the control unit determining that thesecond appropriate time has been reached to switch from the second modeback to the first mode, the coolant switch arrangement switches theoutdoor heat exchanger portion of the data cooling system back to thefirst heat transfer fluid.
 16. The system of claim 15, wherein: thefirst heat transfer fluid comprises water; and the second heat transferfluid comprises one of antifreeze and an antifreeze-water mixture. 17.The system of claim 15, wherein the antifreeze comprises ethylene glycoland the antifreeze-water mixture comprises an ethylene glycol-watermixture.
 18. The system of claim 15, further comprising: a single looppassing through the data center to the outdoor heat exchanger portion; afirst tank to store the first heat transfer fluid; and a second tank tostore the second heat transfer fluid; wherein the coolant switcharrangement comprises a valve arrangement configured to: isolate thefirst and second tanks during steady-state operation; allow the firstheat transfer fluid to flow from the single loop into the first tank andthe second heat transfer fluid to flow from the second tank into thesingle loop when transitioning from the first mode to the second mode;and allow the second heat transfer fluid to flow from the single loopinto the second tank and the first heat transfer fluid to flow from thefirst tank back into the single loop when transitioning from the secondmode to the first mode.
 19. The system of claim 15, further comprising:an indoor loop passing through the data center to a liquid-to-liquidheat exchanger; an indoor-outdoor loop passing from the liquid-to-liquidheat exchanger to the outdoor heat exchanger portion; a first tank tostore the first heat transfer fluid; and a second tank to store thesecond heat transfer fluid; and wherein the coolant switch arrangementcomprises a valve arrangement configured to: isolate the first andsecond tanks during steady-state operation; allow the first heattransfer fluid to flow from the indoor-outdoor loop into the first tankand the second heat transfer fluid to flow from the second tank into theindoor-outdoor loop when transitioning from the first mode to the secondmode; and allow the second heat transfer fluid to flow from theindoor-outdoor loop into the second tank and the first heat transferfluid to flow from the first tank back into the indoor-outdoor loop whentransitioning from the second mode to the first mode.
 20. The system ofclaim 15, further comprising: a first heat transfer fluid indoor looppassing through the data center; a liquid-to-liquid heat exchangerselectively coupled to the first heat transfer fluid indoor loop; afirst heat transfer fluid indoor-outdoor loop selectively connectable tothe first heat transfer fluid indoor loop and coupled to the outdoorheat exchanger portion; and a second heat transfer fluid loop passingfrom the liquid-to-liquid heat exchanger to the outdoor heat exchangerportion; wherein the coolant switch arrangement comprises a valvearrangement configured to: couple the first heat transfer fluid indoorloop to the first heat transfer fluid indoor-outdoor loop duringsteady-state operation in the first mode; and couple the first heattransfer fluid indoor loop to the liquid-to-liquid heat exchanger duringsteady-state operation in the second mode.